A great variety of mechanical systems are controlled by cables, push rods or other such elongated force-transmitting members. Control systems of this type are very widely employed in many vehicular applications and also in many industrial applications, such a machine tools, manufacturing equipment and materials handling systems. For reasons of safety and/or process control, it is often desirable to lock out or otherwise immobilize such control systems. One example typical of such applications is the brake transmission safety interlock (BTSI) system utilized in automobiles. A system of this type operates to prevent a vehicle's transmission from being taken out of the "park" position if the braking system is not activated. The object of employing a BTSI system is to prevent run away acceleration of the vehicle when the gears are shifted. In a typical BTSI system, the shift linkage has a cable-activated locking latch associated therewith. This latch must be released, typically by activating a button associated with the shifter and communicating with the latch by a cable or push rod, before the transmission may be shifted out of the "park" position. BTSI systems further include some type of immobilizing device associated with the cable and communicating with the brake system. The immobilizing device prevents movement of the cable and hence, release of the latch if the brake system is not activated.
One typical prior art cable immobilizing system is shown in U.S. Pat. No. 4,887,702 which describes a typical latch mechanism as well as a particular solenoid-controlled BTSI system. In this system, the latch release cable is associated with the plunger of a solenoid and activation of the solenoid draws the plunger and cable into the solenoid coil thereby preventing further motion of the cable. In its unactivated state, the plunger, and hence the cable, is free to move back and forth.
It has been found, in accord with the present invention, that a solenoid is not the optimum device for this type of application. In general, solenoids are operative to provide motion whereas the object of a BTSI system is to immobilize the latch release cable and such immobilization is more advantageously carried out by means of an electromagnet. A solenoid generally has lower holding power than an electromagnet of comparable size and weight. Consequently, solenoid-based cable immobilization systems are larger and consume more raw materials and more power in operation than do electromagnet based systems.
Prior art cable immobilization systems have the further disadvantage of requiring assembly of the immobilizing device around and on to the cable. This unduly complicates the incorporation of such devices into vehicles or other complex articles of manufacture. It would clearly be desirable to have a cable immobilizing device which can be provided in a finished form and simply retrofitted or otherwise attached to a cable without the necessity for any disassembly of the cable assembly or the holding device.
The present invention overcomes the problems of the prior art by providing an electromagnet-based cable immobilizing device which is smaller in size and has higher holding power than previously employed apparatus. Furthermore, the holding device of the present invention may be completely manufactured in advance and subsequently fitted onto a cable. The small size, high power and simple installation of the present cable immobilizing device readily adapt it to a variety of applications, both in vehicles and in connection with a number of other systems. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.